Method of removing excess impregnant from impregnated wood



Patented Sept. 15, 1953 umn-:o STATES@ PATENT ortica ivrsrnon or: anmfslzlnxcsss IMPREG- r I Nam* FROM IMPREGNATED WGDY Manie snudsmi, Spartanburg-s o No Drawing: Application OotoheltZi, 19.43;,

Sbl'itl N0. 122185?" s. oisans, (c1. 11i-noz) y l y n This; invention relates particularlyu to, the rel maval 1 oi excess `ixnpregnant from impregnated: wood, such aswood' that has been subiected to;- a preservative. treatment, for the purpose'y ot' minimizing' subsequent bleeding of impregnant" ontosthe. surface oi thetr'eated: wood, and' this aptplication is a continuation-impart of myA co pend-ing application Serial# No. 602,687;` nled June 3U, 1914.5,f allowed September 16?, 1949; and now abandoned. i In the preserving` of wood by impregnation with chemicals such asf creosote, there` hash long existed'y a.` major commercial problem of removing the excess immegnant or otherwise pre@` venting: the treated wood from 'bleeding. This bleeding or exudingf or the creosote onto the outer surface of the treated wood commonly occurs during the subsequent commercial use of the treated product, such as: for example creosoted telephone poles and railroad cross-ties` It1 presento an objectionable wet or sticky surface that interferes with the successful and intended use. ot the treated wood product. Creosoted' tellephone poles create `a particular problem si-nce they are commonly installed in locations where the wet creosote on a pole which has bled may easily soil the clothing or other property of per-Y sons who must pass rthe pole, so that it presents aoonsta'nt public annoyance. For this reason creosoted poles `are now prohibited in sections o! l certain cities.' Many Vprior attempts'thave been made to overcomeths bleeding characteristic but' no adequate solution to this problem has heretofore .been provided.

l In accordance with the present invention, I have 4discovered that'` by subjecting the Wood (previously impregnated with a. preservative such ascreosotel to an atmosphere of highly heated organic vapor, the! excess impregnant is substantially and effectively removed, not only from the outer surface of the wood but also from the outer layers of the Wood bers. As a resultI of `this treatment, the surface: of the treated wood is stripped clean, and the removal of the excess impregnant adjacent the surface substantiallyy minimizesthel usual tendency for the impreg' nant vto bleed onto the outer Vsurface during the subsequent commercial use of the treated wood. The method of my invention may be applied to any and all types of wood or other material impregnated with'preservatives or other compounds that form an excess deposit of the impregnant on the surface of the treated material atthe time of or subsequent to the impregnation treatment. lIIX the 1358 0f massive forms OWOOQ 2; y suchas poles,y cross-ties, and lumber for con: struction of bridges, piles;` eter, the impregnation treatment may advantageously be carried out by the well known RueningY process. This process and the equipment for carrying it out are disclosed in: ltliaxv Rueping; S., Patents Nesi '7x-Q9t7a99, grantedy september,- 23, 19021;;` Reissue 12,10% granted October 22, 1:9051;` and 1t00,886,4 granted November 14, ion.

My method of. treating-the impregnatedV wood may follow immediatelyy atterthe last step) the alcove Ruepingprocessthat is, when the creosoted wood is: ready to.: be; removed trol-1,1y the tyleinder in which, theoreosote impregnating treat-l t ment hasA been carriedout. `By suitable modoaf tionl of? the Rzueping; cylinder, the tneated" wood may remain, inthat cylinder` andthefhighly heat-fl ed organic vapor, which I use, passed, intothe cylinderand brought into cleaning; contactA with the: freshly; creosoted wood. I-Loimever,J procl-l ess` may be carried out later, desilredandl equipment separate` from the Ruepingv apparatus.

apparatus suitable for carrying;- out:` the, method; ot my present. invention is disclosed inmyf copending' application Serialel No." 57985-1? led February 2c, now U. s. Patent No.4 2;e35,2:1&. In: that application, the apparatus is. used for drying.: green` or wet wood with organic vapor. This orA some conventional dryingtreat, menti. such. as yard drains or kiln ordina would normally be. carried out on the wood; before it is impregnated with creosote orA other preserva-V the; wood afer the water hasy been removed therefrom by the. drying operation, are then capable, of t takingun substantial amounts. of the oreosotl-if` or other impregnant. l

, if the prior drying operation is carried` out in my above :mentioned apparatus, the Subsc. quent impregnation and cleaning operations may then follow in the same equipment. An alternative procedure would be to impregnato the dried wood in s` Rueping cylinder. and then place theimpregnated wood in my above mentioned apparatus and carry out `the cleaning operation therein with the hot organic vapor. V

The operation of my method involves the heating of the impregnated Wood with the hot or, sonic vapor `which performs the dual function of expanding the cellular structure in the Outer layers of the wood and theimpregnant 'therein so that it is forced Vto the surface of the wood;

from the surface of the Wood by solvent action of the organic vapor as it condenses on the cooler surface area of the wood, which condensate and extracted excess impregnant may be readily drained from the wood and recovered separately from the organic compound or solvent being vaporized for heating the impregnated wood. As a result, this method has the unique feature of providing a continuously fresh spuply of organic solvent condensate for extracting the excess irnpregnant, so that the extracting medium is always maintained at fullstrength in marked contrast with the usual liquid phase extraction methods.

The type of compound used for thev organic organic compounds that will not deleteriously affect the wood or other material treated but will function, as described hereinabove, both to expel the excess impregnant from the outer layer of the material bei-ng treated, and to extract and remove the excess impregnant from the surface of the material; the organic vapor being further characterized by being heated to a Atemperature suiciently high to swell the outer layer of the material or the excess impregnant therein and to enable it to be extracted and become transported away from the material. In addition-to the abover examples of hydrocarbons, the

vapor and the operating temperature thereof .will .Y

isv being .y revary with the impregnant which The followmoved in the cleaning operation.

ing illustrative but non-limiting examples r'of materials and procedures which I have used with success, are given for a more detailed understanding of my' invention. i

Example I Telephone poles were impregnated with creosote by the conventional Rueping process, using commercial creosote which contains a wide range of fractions from low boiling up to heavy tars and oils. The excess creosote was removed practically and effectively, in accordance with this example, by subjecting the creoscted poles to Ian atmosphere of the selected organic vapor. In this example the vapor was obtained by heating light, low boiling fractions of creosote. Satisfactory fractions are those having initial boiling points of between 240 F. and 320 F. or somewhat higher. y

In this specific case, la creosote fraction having a boiling point of approximately 270 F. was used. The hot vapor of this material was passed into the cylinder containing the creosoted poles and the vapor thus brought into intimate contact with the poles on whichA the vapor condensed to form a liquid extractant for the excess creosote. This treatment was continued for about half an hour to one hour until the temperature of the cylinder reached the boiling point of the liquid extractant. The flow of hot vapor was vthen stopped, and la vacuum'of about 20-26 inches was applied on the cylinder for about minutes. This vacuum treatment removed the condensed extractant from the surface of the wood. At the end of this treatment, the vacuum rwas broken and the cylinder and poles were allowed to cool.

After cooling, the poles were removed and were ready for commercial use.` The surface of these poles was stripped clean of the excess impregnant normally remaining on the surface and in the exterior layers of the poles, and bleeding didl not occur in subsequent use of the poles.

Example II in this case being one hour and the vacuum treatment being carried out for a half an hour. The

cross-ties so treated were clean of excess impregnant and did not bleed subsequently. l

The'term organic vapor as used herein is 1ntended to cover any and all. suitable vapors of organic vapor may be obtained from one or more of the following: Coal tar and light petroleum fractions, e. g., benzene, toluene, xylene, and

mesitylene; the coal tar fractions containing these compounds being generally designated as benzol, toluol, xylol, and high flash naphtha. Examples of petroleum fractions Iare those containing heptane through dodecane, which comprise the group commonly included in the range from V. M. P. naphtha through `Stoddard solvent. In addition to the above example of commercial. creosote for the preservative or impregnant, the. following compounds may also be used: Synthetic resins, waxes, asphalt, and pitches.

The temperature range of from about 240 F.y to 320 F., as specified in the above examples; for` the boiling point of the organic compound or solvent used in carrying out the vapor treatment of the present invention, is the practical operating. range and will be found to cover lsubstantially all the compounds that may be usefully employed in the process under normal conditions. The upper limit is determined by the fact that the temperatures reached during the process should not be high enough to lcause damage to the wood, which would occur at about 400 F., and which places a preferable upper vlimit Von the boiling point of the organic solvent used at about 320" F., as noted above. A solvent having a somewhat higher boiling point may be used, as already mentioned, if special circumstances in a given instance make this particularly desirable, but usually better results will be obtained if the upper temperature limit of 320 F. is closely observed. i

The lower temperature limit is determined in the usual case by the fact that with the lower boiling solvents correspondingly low flash points are encounteredfwhich beyond a 'certain point render the process unduly hazardous. reason, it is recommended that-the process not be operated with a solvent' boiling below the above indicated lower limit of 240 F., unless the solvent used is a noninflammable type, such as perchlorethylene. A temperature of 240 F. indicates, ac-

cording to the empirical rule developed by the' petroleum industry, a flash point of about 50 to 55 which is a minimal value if proper safety precautions are observed in a processing operation of this sort.

Of course if a noninflammable type of solvent;

is used, the'limitations imposed by these safety considerations are eliminated, and the lower' temperature limit then becomes a matter simply of providing adequate heating to effect the dev sired expansion and extraction of the impregnant. However, under these circumstances the practical operating temperature range will usual-" 1y remain approximately the same because ofthe necessity for using elevated temperatures to-'obtain effective heating. For example, preservaf tiveiimpregnation of wood with creosote is generally-carried out at a V,temperature of about 180 For this acuasev to 200 F., so that the wood will have been heated to a temperature of this order during the impregnation treatment and it` will consequently be necessary to employ an operating temperature of` from 25 to 50 F. higher at the least in order to obtain any material effect in expansion of the impregnant in the outer layers of` the wood.`

`Between the above noted limits, as long as the orgariie..compound used is a solvent for the particular impregnant to be removed, and boils -at a temperature sufficiently high to heat the impregnated material so that excess impregnant in the outer layers of the material is expanded or i swelled and thereby forced to the surface of the material, the organic compound may otherwise be selected on the basis of such practical factors as cost. relative effectiveness, ease of handling, and the like.

It should also be noted that the above recommended temperature range of from about 240 F. to 320 F. for the boiling point of the organic solvent used, assumes that the process is operated at atmospheric pressure. This will usually ,be the case as a matter of convenience, and also because the vapors of organic solvents suitable for use in the process are characteristically several times heavier than air which makes it possible to expel air from the system by venting it to the atmosphere (at an appropriate point in the solvent recoveryl line, for example), and thereby avoid the danger of damage to the wood through oxidation at the elevated operating temperatures.

On the other hand, if it were particularly desired to use a certain solvent having a boiling point substantially above the recommended'temperature range, this could be done by operating the process under vacuum. For example, a creosote fraction boiling at 450 F. could under a. 24-inch vacuum be made to boil at about 320 F. Evidently, too, the boiling point of a low boiling solvent might be raised to come within the recommended temperature range by operating the process under pressure, although this would not usually be desirable because of the `above noted hazard involved in handling the more highly volatile, low boiling solvents. The irnportant point to notice, however, is that the temperature limitations recommended above should be understood to correspond to the pressure in the closed space used for carrying out the process, and while the process will normally be carried out more conveniently at atmospheric pressure, vacuum or pressure conditions could obviously be established to obtain fully comparable results with organic solvents having divergent boiling points.

I claim:

1. The method of removing excess impregnant from wood subjected to preservative treatment and thereby minimize bleeding of the impregnant onto the surface of the treated wood, which comprises heating the treated wood in a closed space by introducing into said closed space vapors of an organic solvent for the preservative impregnant having a boiling point within the range from about 240 F. to 320 F., and continuing introduction of said organic solvent vapors until the temperature in said closed space reaches the boiling point of said organic solvent, whereby the excess impregnant in the outer layers of thewood is expanded and forced to the surface of the wood, and said excess impregnant is extracted by condensate of said organic solvent formed on vthe surface of the wood in said closed space.

CII.

from wood subjected to preservative treatment and thereby minimize bleeding offthe irmre'g-l nant ontothe surface of the treated wood, which comprises heating the treated" Wood in a closed space by introducing into 'said closed space vapors of an organic` solvent for the preservative" impregnant having a` boiling 'point within the' range from about 240"- F.- to 320 F., continuing=` introduction'. of said organic solvent vapors until the temperature in said closed space reaches the boiling point of said organic solvent, whereby the excess impregnant in the outer layers of the wood is expanded and forced to the surface of the wood, and said excess impregnant is extracted by condensate of said organic solvent formed on the surface of the wood in said closed space, and then impressing a vacuum on said closed space following heating of the wood to remove all condensed extractant from the surface of the wood.

3. The method of removing excess impregnant from wood subjected to preservative treatment with creosote and thereby minimize bleeding of the creosote onto the surface of the treated wood, which comprises heating the creosote treated wood in a closed space by introducing into said closed space vapors of a light creosote fraction having an initial boiling point within the range from about 240 F. to 320 F., and continuing introduction of said vapors until the temperature in said closed' space reaches the boiling point of said light creosote fraction, whereby the excess creosote impregnant in the outer layers of the wood is expanded and forced to the surface of the wood, and said excess creosote impregnant is extracted by condensate of said light creosote fraction formed on the surface of the wood in said closed space.

4. The method of removing excess impregnant from wood that has been subjected to an impregnation treatment and thereby minimize subsequent bleeding of the impregnant onto the surface of the treated wood, which comprises heating the treated wood in a closed space by introduclng into said closed space vapors of an organic solvent for the treating impregnant having a boiling point within the range from about 240 F. to 320 F. at the pressure in said closed space, and continuing introduction of said organic solvent vapors until the temperature in said closed space reaches the boiling point of said organic solvent at the pressure in said closed space, whereby the excess impregnant in the outer layers of the wood is expanded and forced to the surface of the wood, and said excess impregnant is extracted by condensate of said organic solvent formed on the surface of the wood in said closed space.

5. The method of removing excess impregnant from impregnated wood and thereby minimizing subsequent bleeding of the impregnant onto the surface thereof, which comprises heating the impregnated wood in a closed space by introducing into said closed space vapors of an organic solvent for the impregnant having a boiling point at the pressure in said closed space not higher than about 320 F. so that said heating is carried out at 'a temperature substantially below the temperature at which said wood would be damaged by heating, but said boiling `point being not less than 25 F. to 50 F. higher than the initial temperature of said impregnated wood whereby said wood is heated by said vapors so that excess impregnant in the outer layers of the wood is 7 8 effectively expanded andiorced to the-surface .f References Cited-in the file of this patent 0f Said WOOd, Continuing introduction Of Said l UNITED STATES PATENTS organic solvent vapors until said eXcess-impreg-` f Y nant is extracted to a desired extent by con- Number y Name -4 Date densate of said organic .solvent continuously 5 322521 i Clark July 21 1885 formed on the surface of said wood in said closed 649155 [gcnm May 8 1300 space for solvent action yat full strength, and Tewtr g lgg draining and recovering said condensate and eX- 12486804 Fs gre Jn' 15 i924 tracted excess impregnant from said wood. 1181036 l Booty et al May 24J 1938'.

MONIE S. HUDSON. 10 

5. THE METHOD OF REMOVING EXCESS IMPREGNANT FROM IMPREGNATED WOOD AND THEREBY MINIMIZING SUBSEQUENT BLEEDING OF THE IMPREGNANT ONTO THE SURFACE THEREOF, WHICH COMPRISES HEATING THE IMPREGNATED WOOD IN A CLOSED SPACE BY INTRODUCING INTO SAID CLOSED SPACE VAPORS OF AN ORGANIC SOLVENT FOR THE IMPREGNANT HAVING A BOILING POINT AT THE PRESSURE IN SAID CLOSED SPACE NOT HIGHER THAN ABOUT 320* F. SO THAT SAID HEATING IS CARRIED OUT AT A TEMPERATURE SUBSTANTIALLY BELOW THE TEMPERATURE AT WHICH SAID WOOD WOULD BE DAMAGED BY HEATING, BUT SAID BOILING POINT BEING NOT LESS THAN 25* F. TO 50* F. HIGHER THAN THE INITIAL TEMPERATURE OF SAID IMPREGNATED WOOD WHEREBY SAID WOOD IS HEATED BY SAID VAPORS SO THAT EXCESS IMPREGNANT IN THE OUTER LAYERS OF THE WOOD IS EFFECTIVELY EXPANDED AND FORCED TO THE SURFACE OF SAID WOOD, CONTINUING INTRODUCTION OF SAID ORGANIC SOLVENT VAPORS UNTIL SAID EXCESS IMPREGNANT IS EXTRACTED TO A DESIRED EXTENT BY CONDENSATE OF SAID ORGANIC SOLVENT CONTINUOUSLY FORMED ON THE SURFACE OF SAID WOOD IN SAID CLOSED SPACE FOR SOLVENT ACTION AT FULL STRENGTH, AND DRAINING AND RECOVERING SAID CONDENSATE AND EXTRACTED EXCESS IMPREGNANT FROM SAID WOOD. 